Atmospheric corrosion resistant notch ductile high tensile strength steel



Sept. 6, 1966 TADASH] OHTAKE ET AL. 3,271,138

ATMOSPHERIC CORROSION RESISTANT NOTCH DUCTILE HIGH TENSILE STRENGTH STEEL Filed March 12, 1962 Exposed period in years IN VEN TOR.

Tadashi Ohfake Toru Mu to By Takashi Zaizen Tadashi Ni 5 hi Z Mg ZJZY increasing resistance to atmospheric corrosion.

United States Patent 3,271,138 ATMOSPHERIC CORROSION RESISTANT NOTCH DUCTILE HIGH TENSILE STRENGTH STEETJ Tadashi Ohtake, Tobata, Toru Muta and Takashi Zarnen,

Yawata, and Tadashi Nishi, Wakamatsu, Japan, assignors to Yawata Iron & Steel (10., Ltd., Tokyo, Japan, a corporation of Japan Filed Mar. 12, 1962, Ser. No. 179,099 Claims priority, applizationgapan, Mar. 17, 1961,

lClaim. 61. 75-125 This invention relates to an atmospheric corrosion resistant notch ductile high tensile strength steel.

Nickel is generally in such small amount in natural resources and so costly that any atmospheric corrosion resistant high tensile strength steel which contains much nickel cannot help being costly.

The object of the present invention is to provide an atmospheric corrosion resistant high tensile strength steel which contains no nickel, has a tensile strength of 60 to 75 kg./mm. a yield strength of not less than 45 kg./mm. an elongation of not less than 15% with a test piece 25 mm. thick and of a guage length of 200 mm. as rolled, a low sensitivity to notch brittleness and an atmospheric corrosion resistance twice as high as ordinary carbon steel. Said steel is a cheap low alloy atmospheric corrosion resistant notch ductile high tensile strength steel containing 0 to 0.20% carbon, 0.01 to 1.0% silicon, 0.2 to 2.00% manganese, 0 to 0.10% phosphorus, 0.20 to 0.60% copper, 0 to 1.0% chromium, 0.027 to 0.5% titanium and 0.05 to 0.5% niobium, the rest being iron and impurities, the above percentages being by weight based on the total weight of the steel.

The figure shows curves representing the results of exposure tests of mild steels and steels according to the present invention when carried out on the roof of a building wherein the weight loss due to corrosion is measured in g./d'm.

The reason why the respective component elements in the present invention are in the amounts as mentioned above are as follows: when carbon is more than 0.2%, the cold-workability and weldability will deteriorate, therefore, the upper limit is set at 0.2% and the lower limit at 0%, because, even with 0.09%, the expected mechanical properties will be obtained as shown in Table 1. It is known that copper is an important element in However, unless the content is m-ore than 0.2%, it will not be etfective. The content is less than 0.6%, because, when the copper content is greater, it will show an ageing eflect and will be likely to cause surface cracks when it is hot-rolled. In the present invention copper is also contained as an element for increasing atmospheric corrosion resistance. Silicon is added for deoxidation and is contained within a range of 0.01 to 1.0% depending on the steel making process. Manganese is for deoxidation and also increases the yield strength and tensile strength. with less than 0.2% manganese, these effects will not be apparent. Therefore, the lower limit is set at 0.2%. The upper limit is set at 2.0%, because, above it, the coldworkability and weldability of the steel will be impaired. It is known that, when phosphorus coexists with copper, it will increase the atmospheric corrosion resistance. It will also increase the tensile strength. However, if too much phosphorus is added, the product will become brittle. Therefore, the upper limit is set at 0.10%. The lower limit is set at 0%, because, even when the amount of phosphorus is 0.04%, the expected mechanical properties and atmospheric corrosion resistance will be obtained as shown in Table l by a proper combination of the component elements. Titanium will further improve the atmospheric corrosion resistance of a low copper steel. In

Patented Sept. 6, 1966 the figure, A represents a mild steel in a composition range of 0.05% C, 0.01% Si, 0.38%, Mn, 0.31% P and 0.18% Cu. B and C represent atmospheric corrosion resistant high tensile strength steels Nos. 4 and 1 in Table 1, respectively. The conventional high tensile strength steel is a steel which has a yield strength of more than 33 kg./m'm. and .a tensile strength of more than 50 kg./mm. and is obtained by having a manganese content of more than 1.0%. 'In the steel according to the present invention, even if the manganese content is less than 2.00% and the carbon content is made as low as possible, a tensile strength of 60 to kg./rnm. a yield strength of more than 45 kg./mm. and an elongation of more than 15% will be obtained owing to the effect by titanium. When the carbon content is less than 0.20% and the manganese content is less than 2.0%, the weldability is so high that the product can be welded without preheating. The upper limit of the titanium content is set at 0.5%, because, even if more than that is added, the effect on the atmospheric corrosion resistance will be small and, further, the addition of too much titanium is not desirable to the mechanical properties. The lower limit of the titanium content is 0.027% because, below said limit, the ettect of improving the atmospheric corrosion resistance will be small and any increase in strength will hardly be noticed. Chromium is used to increase the yield strength and tensile strength and to improve the atmospheric corrosion resistance and is therefore added as required. The upper limit of chromium is set at 1.0%, because, if more chromium than that is added, the workability and weldability is likely to be reduced.

A feature of the present invention is the addition of niobium. When niobium is added and the rolling conditions are properly selected, the resistance of this kind of atmospheric corrosion resistant high tensile strength steel to notch brittleness represented by the V notch Charpy impact value of the hot-rolled steel is further improved as shown in Table 2. With less than 0.05% niobium, the effect will not be obvious. Therefore, the lower limit is 0.05%. The upper limit is 0.5%, because, even if more niobium is added, the effect of improviding the impact property will not be great.

The product of the present invention is to be used mostly as hot-rolled steel. As described above, its mechanical properties are higher than of any conventional high tensile strength steel. Specifically, while it has a high strength, its sensitivity to notch brittleness ice is lower. Its atmospheric corrosion resistance is also very much higher than of the ordinary carbon steel.

TABLE 1 No. C Si Mn P Cu Cr Ti Nb 0. 37 1. 48 0. 062 0. 33 0. 40 0. 10 0 15 0. 23 1. 09 0. 057 0. 40 0. l9 0. 07 0 19 0. 29 1. 50 0. 068 0. 29 0. 37 0. 08 0 28 0. l5 1. 27 0. 039 0. 34 0. 55 0. l3 0. 16 0. 42 l. 61 0. 041 0. 45 0. 43 0. l6 0. 23 0. 09 1. 25 0. 058 0. 33 0. 05 0. 08 0. 13 0. 31 1. 38 0. 070 0. 49 0. 31 0. 10 0. 09 0. l9 1. 05 0. 045 0. 36 0. 25 0. 05 0. 16

Elongation in V-notch Oharpy Yield strength Tensile strength percent (GL= impact value (at No in kg./mm. in kg./m1n. 200 mm.) 20 C.) in kg.-

142233 p.s.1. 1422.33 p.s.i. percent elonm./cm. 5,785

gation in 8 ft. lbs

inches 1A"- 52. 6 67. 1 18. 0 4. 9 2A 48. 2 62. 2 21. 0 7. 8 3A.-- 49. 8 62. 6 20. 0 6. 5 4A..- 53. 3 68. 5 18. 5 5. 7 5A 50. 8 66. 3 19. 5 6. 0 6A.-- 52. 4 70. 5 16. 5 3. 5 7A 51. 5 67. 8 l8. 5 5. 3 8A..- 52. 0 70. 8 l7. 0 4. 7

TABLE 2 No. C Si Mn P Cu Cr Ti Nb 1A 0. 12 0.37 1. 48 0.062 0.33 0.40 0. 10 0. 15 1B 0. 12 0. 35 1. 49 0. 065 0. 31 0. 41 0.09 0. 001 5A 0.09 0.42 1. 61 0. 041 0.45 0. 43 0. 16 0.23 513 0, 09 0.43 1. 57 0.043 0. 45 0.42 0. 13 0. 003 6A 0. 17 0. 09 1.25 0. 040 0.33 0. 05 0.08 0. 13 6B 0. 16 10 1. 31 0. 039 0.34 0. 05 0.07 0.003

Elongation in V-noteh Charpy Yield strength Tensile strength percent (GL: impact value (at No. in kglmmfl: in kg./1nm. 200 mm.)= 20 C.) in kg.-

142133 p.s.i. 1422.33 p.s.i. percent elonm./cm. 5,785

gation in 8 ft. lbs

inches 1A... 52.6 67.1 18.0 4. 9 1B 49.5 65.5 18.2 0.8 5A 50. 8 06. 3 19. 5 6. B 49.8 67.1 18.8 1. 2 6A 52. 4 70. 5 16. 5 3. 5 6B 48.8 68.3 17.8 0.7

The yield strength designates the yield point which is observed in the tension test.

What we claim is:

An atmospheric corrosion resistant notch ductile high tensile steel, which has a tensile strength greater than kg./mm. consisting essentially of 0 to 0.20% carbon, 0.01 to 1.0% silicon, 1.05 to 1.61% manganese, 0 to 0.10% phosphorous, 0.20 to 0.60% copper, 0 to 1.0% chromium, 0.027 to 0.5% titanium, 0.05 to 0.5% niobium, and iron, said percentages being 'by Weight based on the total weight of the steel.

References Cited by the Examiner UNITED STATES PATENTS 2,474,766 6/1949 Waggoner et al. 125 2,532,117 11/1950 Newell 75125 2,565,953 8/1951 De Gaspari et al. 75125 DAVID L. RECK, Primary Examiner.

RAY K. WINDHAM, Examiner.

A. M. SANTORO, P. WEINSTEIN,

Assistant Examiners. 

